The visual appearance of painted automotive surfaces (for example, exterior painted automotive surfaces) is an important aesthetic property. Original equipment manufacturer (that is, OEM) and aftermarket industries devoted many resources to the development and application of automotive paint systems that provide aesthetic properties such as, for example, low haze and good distinctness of image.
It is commonplace for automobile manufacturers to use a base coat and clear coat paint system. The base coat provides the desired color, while the clear coat, which is applied over the base coat, provides a transparent scratch/chip-resistant protective coat. Such paint systems typically magnify defects (for example, scratches, haze, and dust nibs) in either the base coat or the clear coat.
One common method for imparting (or restoring) a high quality appearance to an automotive paint system uses a multi-step process.
First the defects are abraded using a coated abrasive product with a fine abrasive particle size (for example, a sandpaper, or a structured abrasive article). This step provides rapid removal of the defects, but typically leaves a scuff (and sometimes scratches) that needs to be removed.
Next, scuffs are removed by buffing using a buffing composition. The buffing composition typically has a liquid vehicle and abrasive particles of typically smaller size than the abrasive particles used in the coated abrasive article. However, depending of the paint system, the buffing step may result in a surface with a hazy appearance.
The hazy appearance is removed by a finishing step in which the hazy portion of the paint system is buffed with a finishing composition. The finishing composition typically has a liquid vehicle and abrasive particles of smaller size than the abrasive particles used in the buffing composition.
Finally, residue from the buffing and/or finishing compositions is removed (for example, with a soft cloth) thereby producing an aesthetically appealing finish substantially free of surface residue.
In general, the cut rate of abrasive particles depends on their composition and particle size. Larger particles typically exhibit a higher cut rate, while very small particles are typically used in order to achieve a low haze. Hence, the reason for multiple steps typically relates, at least in part, to the need for quickly removing defects and achieving a flat smooth surface. This is achieved by using relatively large abrasive particles (which provide a high cut rate) in a first step (or multiple steps), and then using very fine abrasive particles (which have a low cut rate) to achieve a very low haze in one or more subsequent steps. This multiple step combination is most often optimized to achieve a high cut rate followed by a fine finish, all while minimizing the overall time required.